Dual-Zone Temperature-Modulated Growth of PtTe ₂ /Ge Schottky Diodes for High-Speed Broadband Photodetection from Visible to 4.2 μm

Two-dimensional (2D) PtTe₂ films with controlled crystallinity and morphology are synthesized via a dual-zone temperature modulation strategy, enabling tailored growth of low-roughness single-oriented (LRSO, denoting uniaxial preferred orientation), medium-roughness multioriented (MRMO), and high-roughness multioriented (HRMO) PtTe₂. Systematic characterization reveals distinct structural features: LRSO-PtTe₂ exhibits high crystallographic alignment (RMS roughness: 3.9 nm), while HRMO-PtTe₂ displays disordered orientations and elevated roughness (55.9 nm), which is attributed to Te-deficient growth under high-temperature conditions. Leveraging these materials, PtTe₂/Ge heterojunction photodetectors are fabricated, demonstrating broadband detection from visible (532 nm) to mid-infrared (4156 nm). The HRMO-PtTe₂/Ge device achieves responsivity (228 mA W^-1 at 1550 nm) and specific detectivity (2.26 × 10¹¹ Jones), outperforming LRSO-PtTe₂/Ge counterparts due to enhanced light scattering and interfacial strain relaxation. Remarkably, the LRSO-PtTe₂/Ge device exhibits fast response speeds (rise/fall time: 0.84/8.27 μs) and a high 3 dB bandwidth of 0.272 MHz, attributed to its defect-minimized crystalline structure. Both devices enable high-fidelity grayscale imaging via single-pixel mapping, validated under 1550 nm illumination. This work elucidates the interplay between growth kinetics and optoelectronic performance, advancing the development of high-speed, broadband photodetectors for imaging and sensing applications.